The measurements of downhole formation properties surrounding a borehole, such as for example the measurement of the dielectric permittivity of a formation, are known to provide useful information about the formations. The formation properties of different materials forming the formations may vary, so that the measurement of the formation properties can be a useful means for evaluating the formation. Logging methods and tools for this purpose have been developed over the years.
In layered formations, shoulder beds may have undesirable effects on measurement logs performed to estimate formation properties. Shoulder beds effects may be present in thinly laminated formations. In the present description and in the following claims, thinly laminated formations are formations comprising thin laminations, such as for example smaller than 6 inches.
Further, shoulder beds effects may particularly affect measurement logs taken at relatively low frequencies, such as for example lower than 400 MHz.
Original log profiles may be either smoothed with overshoot and undershoot patterns, or distorted. This can lead to an erroneous estimation of the formation properties.
It is therefore desirable to correct any shoulder beds effects so as to obtain accurate measurements of downhole formation properties. In order to correct any shoulder beds effects, a tool response or multiple tool responses in layered formations should be approximated with good accuracy.